1. Field of the Invention
The present invention relates to a coordinate input device which inputs the coordinate position of an operation surface pointed by a finger or pen to a personal computer, and particularly to a coordinate input device which can perform a cursor position control by dragging a finger on an operation surface to input the coordinate and which can perform a switching input operation from the operation surface.
2. Description of the Related Art
It has been widely known that such a coordinate input device uses as a tablet which can detect the coordinate position of a control member such as a finger on an operation plate in response to, for example, a change in an amount of a received light or an electrostatic capacitance. The tablet is a detecting device in a flat shape which detects a coordinate position of a control member every a predetermined short sampling period of time and issues the detection signal to a computer body. The position of the cursor displayed on a display screen can be controlled by dragging the control member (usually, an operator's finger) on the operation surface of the tablet. When an operator touches his finger against the operation surface of the tablet and moves it in the same direction as a direction of the cursor to be moved and by a predetermined movement thereof, a computer issues a control signal to move the cursor on the display screen. In this case, the movement and the moving direction of the cursor can be determined in accordance with the coordinate change of the finger on the operation surface.
Since the operation surface of a tablet is generally much smaller than the screen of a conventional display, the movement of the cursor is determined by multiplying the movement of a control member (finger) by a predetermined qualified value. If the qualified value is constant, the dragging operation on the operation surface is complicated when a cursor is moved largely or finely on a display. For that reason, a current cursor control device using a tablet detects the moving rate of a control member based on a coordinate change of the control member every sampling time, whereby it determines coarsely the qualified value when the moving rate is large or determines finely the qualified value when the moving rate is small. As described above, the qualified value which is a coefficient for converting the movement of a control member into a cursor movement increases and decreases in accordance with the moving rate of the control member. Therefore an operator can control the position of the cursor with the movement quite larger than that of a finger by moving swiftly it on the operation surface when he wants to move largely the cursor on a display screen. In similar manner, an operator also can control the position of the cursor at the same movement as that of his finger by moving slowly his finger on the operation surface when he wants to move finely the cursor on a display screen.
The conventional cursor control device where a qualified value (conversion coefficient) is varied in accordance with the moving rate of a control member on the operation surface of a tablet can improve its operability in comparison with a fixed qualified value using device. However, actually, it is not easy to vary properly the moving rate of the control member such as a finger on an operation surface. The operability is not necessarily good because it is unexpectedly difficult to control the moving rate of the control member. Particularly, with a narrow operation surface of a tablet because of a limited space, it is more difficult to control the moving rate of the control member through the qualified value must be varied largely, thus causing poor operability.
The above tablet can input coordinates to a personal computer. However, when an icon at a specified position on a display is selected, a special pen with a switch mounted on its tip thereof must be used or a push-button switch mounted separately from the operation surface for coordinate inputting must be depressed after the finger inputting a coordinate has been left off from the operation surface. Accordingly, the conventional tablet provides poor operability.